1. Field of the Invention
The invention relates to novel bleach activators, bleaching compositions containing these activators, and to a method of bleaching laundry fabrics using a composition comprising these novel bleach activators.
2. Prior Art
Active oxygen-releasing compounds are well known as effective bleaching agents. These compounds are frequently incorporated into detergent compositions for stain and soil removal. Unlike the traditional sodium hypochlorite, hydrogen peroxide-releasing compounds are less aggressive and thus more compatible with the ingredients of detergent compositions. On the other hand, the bleaching activity of these compounds is highly temperature dependent. Use of hydrogen peroxide releasing bleaches is only practical where the wash temperatures are above 60.degree. C. Below this temperature, extremely high amounts of the active oxygen-releasing compound must be added to achieve the desired result. Frequently, wash temperatures are, however, on the low side for various reasons including that of energy efficiency.
The temperature problem can be solved by use of transition metal containing compounds which catalyze or activate the oxygen-releasing material, even at relatively low temperatures. Typical metals known in the art include those of iron, cobalt, manganese and copper. Only select transition metal substances provide the efficient catalysis necessary for laundry fabrics application at these temperatures. Furthermore, not all types of stains are removable by the transition metal-hydrogen peroxide generated substances. Especially difficult to bleach are hydrophobic stains such as those caused by spaghetti sauce and the like.
It is known in the art that peroxygen compounds (i.e., peracetic acid) may act as effective bleaching agents when combined with polypyridine chelating agents in the presence of transition metal cations having atomic number 24-29 (i.e., Cr, Mn, Fe, Co, Ni or Cu) at temperatures as low as 49.degree. C. (U.S. Pat. No. 3,532,634). It is also known that no transition metal need be added and bleaching can be obtained at temperatures as low as 30.degree. C. when certain pyridine chelators (i.e., 2,2'-bipyridine) are added to a bleaching solution containing peracetic acid. Rucker et al, Tex. Res. J., 58003: 148-160 (1988). No transition metal cations need be added because these cations are naturally present in the scoured cotton fibers which are bleached as taught by this reference. Neither of these references teaches the use of molybdenum or tungsten complexes as bleach activators.
Peroxometallate compounds (wherein the metal is molybdenum or tungsten) are known to catalyze the reaction of peroxide with alkenes and alcohols, i.e., functionalities commonly found in stains. (Minoun et al, Tetrahedron, 26: 37-50 (1970); French Publication No. 2187774 (Minoun et al);French Publication No. 2106975 (Barrat et al); European Publication No. 0179664 (Atlantic Richfield Co.)). However, these compounds have not been previously used as stain removal catalysts against complex polyalkene or polyalcohol stains.
Thus it would be useful to find a novel class of stain removal catalysts to be used in laundry fabric cleaning. Moreover, it would be useful if the stain removal catalyst could be readily modified (e.g., by choice of ligating group) to affect the efficiency of the catalyst.